1. Field of the Invention
This invention relates to venting devices, and more particularly to a vent valve that is installed in a liquid-containing tank, such as a liquid fuel tank, and that is constructed so that it permits the passage therethrough of gases or vapors, but prevents the passage therethrough of liquid from the tank.
2. Description of the Related Art
Venting devices are normally utilized in liquid-containing tanks in order to permit the gas or vapor pressure within the tank to be equalized with the pressure of the surrounding air. The vents function to permit escape into the atmosphere of a sufficient quantity of higher than ambient pressure gas or vapor to lower the internal pressure within the tank, and permit entry into the tank of ambient air when the pressure in the tank is lower than the ambient pressure, to thereby avoid the imposition upon the walls of the tank of the stresses that would otherwise result from expansion and contraction of the gas or vapor within the tank as a result of temperature changes. Additionally, where a tank is provided that is subject to being tilted, such as a liquid fuel tank carried by a vehicle that traverses hilly terrain, some provision must be made to prevent passage of the liquid fuel through the vent valve, in order to reduce the fire hazard and also to reduce hydrocarbon emissions into the atmosphere. An example of a vehicle in which such a venting device is desirable is a gasoline-powered golf cart which is intended to be operated on slopes common to golf courses. During the operation of such golf carts, the vertical axis of the fuel tank is oftentimes tilted as a result of the uneven terrain.
Various types of vent valve structures have been devised to respond to the tilted fuel tank situation referred to above, but most of those solutions have involved complicated, difficult to manufacture, and therefore costly vent valve structures. For example, in U.S. Pat. No. 4,702,268, which issued on Oct. 27, 1987, to Kurt Armbruster et al., there are shown various types of vent valve structures utilizing a plurality of ball-shaped masses for controlling the flow of gases and liquids through the valve.
It is an object of the present invention to provide a vent valve structure for a liquid-containing tank, wherein the vent valve is of simplified construction.
It is another object of the present invention to provide a vent valve structure in which a pair of balls of different size and different weight are provided, one of the balls serving as a valve member to block a vent opening.
It is a still further object of the present invention to provide a vent valve structure that is capable of being made from inexpensive materials and at a low manufacturing cost.